本文提供了20个实用的Java代码片段，包括字符串与整数互转、向文件追加内容、获取当前方法名等，帮助开发者提高编程效率。
下面是20个非常有用的Java程序片段，希望能对你有用。
1. 字符串有整型的相互转换
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String a = String.valueOf( 2 ); //integer to numeric string
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int i = Integer.parseInt(a); //numeric string to an int
2. 向文件末尾添加内容
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BufferedWriter out = null ;
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try {
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out = new BufferedWriter( new FileWriter(”filename”, true ));
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out.write(”aString”);
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} catch (IOException e) {
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// error processing code
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} finally {
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if (out != null ) {
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out.close();
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}
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}
3. 得到当前方法的名字
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String methodName = Thread.currentThread().getStackTrace()[ 1 ].getMethodName();
4. 转字符串到日期
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java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
或者是：
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SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );
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Date date = format.parse( myString );
5. 使用JDBC链接Oracle
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public class OracleJdbcTest
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{
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String driverClass = "oracle.jdbc.driver.OracleDriver" ;
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Connection con;
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public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
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{
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Properties props = new Properties();
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props.load(fs);
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String url = props.getProperty( "db.url" );
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String userName = props.getProperty( "db.user" );
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String password = props.getProperty( "db.password" );
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Class.forName(driverClass);
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con=DriverManager.getConnection(url, userName, password);
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}
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public void fetch() throws SQLException, IOException
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{
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PreparedStatement ps = con.prepareStatement( "select SYSDATE from dual" );
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ResultSet rs = ps.executeQuery();
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while (rs.next())
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{
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// do the thing you do
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}
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rs.close();
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ps.close();
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}
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public static void main(String[] args)
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{
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OracleJdbcTest test = new OracleJdbcTest();
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test.init();
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test.fetch();
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}
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}
6. 把 Java util.Date 转成 sql.Date
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java.util.Date utilDate = new java.util.Date();
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java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());
7. 使用NIO进行快速的文件拷贝
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public static void fileCopy( File in, File out )
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throws IOException
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{
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FileChannel inChannel = new FileInputStream( in ).getChannel();
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FileChannel outChannel = new FileOutputStream( out ).getChannel();
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try
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{
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// inChannel.transferTo(0, inChannel.size(), outChannel); // original -- apparently has trouble copying large files on Windows
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// magic number for Windows, 64Mb - 32Kb)
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int maxCount = ( 64 * 1024 * 1024 ) - ( 32 * 1024 );
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long size = inChannel.size();
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long position = 0 ;
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while ( position < size )
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{
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position += inChannel.transferTo( position, maxCount, outChannel );
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}
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}
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finally
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{
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if ( inChannel != null )
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{
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inChannel.close();
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}
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if ( outChannel != null )
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{
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outChannel.close();
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}
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}
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}
8. 创建图片的缩略图
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private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)
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throws InterruptedException, FileNotFoundException, IOException
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{
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// load image from filename
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Image image = Toolkit.getDefaultToolkit().getImage(filename);
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MediaTracker mediaTracker = new MediaTracker( new Container());
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mediaTracker.addImage(image, 0 );
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mediaTracker.waitForID( 0 );
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// use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());
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// determine thumbnail size from WIDTH and HEIGHT
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double thumbRatio = ( double )thumbWidth / ( double )thumbHeight;
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int imageWidth = image.getWidth( null );
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int imageHeight = image.getHeight( null );
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double imageRatio = ( double )imageWidth / ( double )imageHeight;
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if (thumbRatio < imageRatio) {
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thumbHeight = ( int )(thumbWidth / imageRatio);
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} else {
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thumbWidth = ( int )(thumbHeight * imageRatio);
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}
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// draw original image to thumbnail image object and
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// scale it to the new size on-the-fly
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BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
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Graphics2D graphics2D = thumbImage.createGraphics();
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graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
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graphics2D.drawImage(image, 0 , 0 , thumbWidth, thumbHeight, null );
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// save thumbnail image to outFilename
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BufferedOutputStream out = new BufferedOutputStream( new FileOutputStream(outFilename));
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JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
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JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);
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quality = Math.max( 0 , Math.min(quality, 100 ));
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param.setQuality(( float )quality / 100 .0f, false );
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encoder.setJPEGEncodeParam(param);
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encoder.encode(thumbImage);
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out.close();
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}
9. 创建 JSON 格式的数据
请先阅读这篇文章 了解一些细节，
并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)
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import org.json.JSONObject;
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...
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...
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JSONObject json = new JSONObject();
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json.put( "city" , "Mumbai" );
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json.put( "country" , "India" );
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...
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String output = json.toString();
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...
10. 使用iText JAR生成PDF
阅读这篇文章 了解更多细节
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import java.io.File;
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import java.io.FileOutputStream;
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import java.io.OutputStream;
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import java.util.Date;
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import com.lowagie.text.Document;
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import com.lowagie.text.Paragraph;
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import com.lowagie.text.pdf.PdfWriter;
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public class GeneratePDF {
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public static void main(String[] args) {
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try {
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OutputStream file = new FileOutputStream( new File( "C:\\Test.pdf" ));
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Document document = new Document();
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PdfWriter.getInstance(document, file);
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document.open();
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document.add( new Paragraph( "Hello Kiran" ));
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document.add( new Paragraph( new Date().toString()));
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document.close();
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file.close();
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} catch (Exception e) {
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e.printStackTrace();
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}
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}
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}
11. HTTP 代理设置
阅读这篇 文章 了解更多细节。
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System.getProperties().put( "http.proxyHost" , "someProxyURL" );
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System.getProperties().put( "http.proxyPort" , "someProxyPort" );
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System.getProperties().put( "http.proxyUser" , "someUserName" );
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System.getProperties().put( "http.proxyPassword" , "somePassword" );
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